Synthesis and Characterization of the New Ternary Titanium Thiophosphate TiP2S7 and Comparison to Ti4P8S29: Synthesis and Characterization of the New Ternary Titanium Thiophosphate TiP2S7 and Comparison to Ti4P8S29

The synthesis of the new thiophosphate TiP2S7 succeeded from TiS2, P4S10, and elemental S in presence of Li2S or elemental Cu and additional S. The crystal structure [orthorhombic, Pbcn, a = 23.9895(13), b = 6.8308(4), c = 19.6295(6) angstrom, V = 1905.0(2) angstrom(3), Z = 8, R-1 = 2.78 %, wR(2) = 6.35 % (all reflections)] consists of edge-connected TiS6 octahedra and PS4 tetrahedra, which form corrugated layers. Each of these layers interpenetrates a second one to form double layers parallel to the bc plane. The highly anisotropic characteristics are macroscopically observed by the easy cleavage property. One S atom coordinating the Ti atom is partially replaced by a S-2 dumbbell leading to a TiS5(S-2) coordination. Including the dumbbell atoms the exact composition of the new compound is refined to TiP2S7.05. According to the crystal structure TiP2S7 shows two signals in P-31 NMR spectra. Another known ternary thiophosphate with a very similar composition, Ti4P8S29, was reinvestigated with special consideration of the S/S-2 occupational disorder, the composition was determined exactly to Ti4P8S28.68 and found to be different from the previously reported.